package com.linlin.shortlink.admin.toolkit;import java.security.SecureRandom;public final class RandomGenerator {    private static final String CHARACTERS = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";    private static final SecureRandom RANDOM = new SecureRandom();    /**     * 生成随机分组ID     *     * @return 分组ID     */    public static String generateRandom() {        return generateRandom(6);    }    /**     * 生成随机分组ID     *     * @param length 生成多少位     * @return 分组ID     */    public static String generateRandom(int length) {        StringBuilder sb = new StringBuilder(length);        for (int i = 0; i < length; i++) {            int randomIndex = RANDOM.nextInt(CHARACTERS.length());            sb.append(CHARACTERS.charAt(randomIndex));        }        return sb.toString();    }}